1. Field of the Invention
This invention relates to an integrated telescoping antenna apparatus wherein a plurality of antenna portions individually acting as different antennas are disposed coaxially and which is used as a shared antenna for transmitting or receiving radio waves of different frequency bands simultaneously or as a diversity antenna for obtaining a diversity effect.
2. Description of the Related Art
A diversity antenna is conventionally known wherein two sleeve antenna portions are disposed at upper and lower stages in a vertical column as disclosed, for example, in Japanese Patent Laid-Open No. 97207/1984. The conventional diversity antenna is constituted such that, in order to prevent a coaxial feeder cable connected to the upper antenna portion and leakage current from having an influence on an impedance characteristic of the lower antenna portion, the coaxial feeder cable for the upper antenna portion extends through the inside of the lower antenna portion and a radio wave absorbing member or a current limiting metal member is mounted between the upper and lower antenna portions. Where such radio wave absorbing member or current limiting metal member is mounted between the upper and lower antenna portions, the two sleeve antenna portions individually function as independent antennas without any deterioration in sensitivity thereof.
With the conventional diversity antenna, however, while leakage current flowing from the upper antenna portion to an outer conductor of the coaxial feeder cable can be cut off, current may possibly leak from an upper end of the lower antenna portion to the outer conductor of the coaxial feeder cable extending through the inside of the lower antenna portion because the radio wave absorbing member or current limiting metal member is mounted in a slightly spaced relationship from both of the upper and lower antenna portions between the upper and lower antenna portions. Here, if current leaks from the lower antenna portion to the outer conductor of the coaxial feeder cable, the impedance characteristic of the lower antenna portion is varied so that the sensitivity thereof is deteriorated. It is to be noted that to prevent leakage current in the present invention signifies to block leakage current which may have a bad influence on the antenna sensitivity.